Magnetic storage apparatus

ABSTRACT

The proposed magnetic storage apparatus has the following features. The frequency at which data is recorded is selected to be 45 MHz. The thickness, resistivity and relative permeability of the magnetic film of which the magnetic poles of the magnetic head used in the apparatus are made are designed considering the eddy current loss. Also, the relation of μd 2 /ρ≦500 is satisfied where d (μm) is the thickness of the magnetic film of which the magnetic poles of the magnetic head are made, ρ(μΩ-cm) is the resistivity, and μis the relative permeability in a low-frequency range. Under these conditions, the amount of attenuation of recording magnetic field is reduced to 10% or below, and problems of writing blur and overwrite value variation which occur as the recording frequency changes can be solved. Moreover, the media data rate is 15 megabytes per sec., and the areal data-recording density is 500 megabits per square inch or more.

REFERENCE TO EARLIER FILED APPLICATION(S)

This application is a continuation of the following earlier filedapplication(s) Ser. No. 09/003,506, filed Jan. 6, 1998, now U.S. Pat.No. 6,064,546, which is a continuation application of U.S. Ser. No.08/422,928, filed Apr. 17, 1995, abandoned.

BACKGROUND OF THE INVENTION

This invention relates to magnetic storage apparatus capable of bothhigh-density recording and high-speed transfer of data at a time, andparticularly to one in which a high areal recording density can beachieved by suppressing the attenuation of the magnetic field intensityat high recording frequencies.

The induction-type thin-film magnetic head mounted on the conventionalmagnetic disk apparatus has its magnetic poles made of a NiFe alloy thinfilm of about 3 μm in thickness. Since the resistivity of this NiFealloy film is as low as around 16 μΩ-cm, the eddy-current loss isincreased at high frequencies so that the recording magnetic fieldintensity is reduced. The amount of writing blur or overwrite value ischanged with the recording frequency under the influence of thiseddy-current loss. As a conventional example, there is, for example,JP-A-58-115612 in which it is described that the generation of eddycurrent affects the low-resistivity permalloy (such as NiFe alloy) insuch a way as to reduce its high-frequency permeability, thus goodreproduction characteristics (sensitivity) are not obtained. Because ofthese problems, the recording frequency at which the NiFe alloythin-film head can operate is limited to about 30 MHz. On the otherhand, the storage capacity of the magnetic disk apparatus has beensteadily increased year after year, up to the extent that the nowavailable 3.5-inch disk storage apparatus has an areal recording densityof 350 Mb/in²maximum. The data recording frequency at which thisapparatus can record is around 27 MHz which is near the limit of theinduction-type thin-film magnetic head using NiFe alloy thin films.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a magnetic storage apparatususing magnetic heads for high-speed access and high-speed transferwithout changing the writing blur or overwrite value as the recordingfrequency changes.

The above object can be achieved by designing the thickness, resistivityand relative permeability considering the eddy current loss in themagnetic pole film of the recording head so as to prevent the writingblur or overwrite value from varying as the recording frequency changes,and by selecting the data recording frequency to be high, and byrotating the magnetic disk fast.

In other words, according to the first invention, there are provided:

(1) a magnetic storage apparatus having means for achieving a media datarate of 15 megabytes per sec. or above and an areal data-recordingdensity of 500 megabits per square inch or above;

(2) a magnetic storage apparatus according to item (1), wherein wheninformation is recorded on a magnetic disk of 3.5-inch diameter orbelow, this disk is rotated at a rate of 4000 rpm or above in therecording/reproduction mode and the recording frequency is selected tobe 45 MHz or above;

(3) a magnetic storage apparatus according to item (1), wherein a metalmagnetic film having a coercive force of 2 kOe or above is formed on themagnetic disk used;

(4) a magnetic storage apparatus according to item (1), wherein the risetime of the recording current is selected to be 5 nanosecond (ns) orbelow;

(5) a magnetic storage apparatus according to item (4), wherein therecording coil 25, 25′ (FIGS. 4,8) of an induction type magnetic headused for recording information on the magnetic disk medium is formed bya thin-film process and has three terminals A, B, C, the inductancebetween the terminals is one microhenry (μH) or below;

(6) a magnetic storage apparatus according to item (5), wherein therecording coil 25, 25′ (FIGS. 4,9) of the induction type magnetic headused for recording information on the magnetic disk medium has adouble-layer structure in which the first layer coil 92 and the secondlayer coil 94 have an equal number of turns but are wound in oppositedirections to each other; and

(7) a magnetic storage apparatus according to item (5), wherein therecording coil 25, 25′ (FIGS. 4,8) of the induction type magnetic headused for recording information on the magnetic disk medium has asingle-layer structure 80 (FIG. 8) in which an intermediate-pointterminal is connected at a mid point (c) between both coil ends (a), (b)which mid point corresponds to half the total number of turns of thecoil, and a current (FIG. 10) flowing between the terminals (c) and (a)is opposite in phase to a current flowing between the terminals (c) and(b).

According to the second invention, there are provided:

(8) a magnetic storage apparatus having means for causing a relation ofμd²/ρ≦500 to be satisfied where d (μm) is the thickness of a magneticfilm which forms the recording magnetic poles of a magnetic head forrecording data or for recording/reproduction of data, ρ (μΩ-cm) is theresistivity, and μ is the relative permeability in a low-frequencyregion;

(9) a magnetic storage apparatus according to item (8), wherein at leastpart of the recording magnetic poles of the magnetic head for recordingdata or for recording/reproduction of data has a multi-layered structureof alternate magnetic layer and insulating layer and the thickness ofthe multi-layered film is 2.7 μm or below;

(10) a magnetic storage apparatus according to item (8), wherein atleast part of the recording magnetic poles of the magnetic head forrecording data or for recording/reproduction of data is made of Co-basedamorphous alloy or Fe-based amorphous alloy;

(11) a magnetic storage apparatus according to item (8), wherein atleast part of the recording magnetic pole material of the magnetic headfor recording data or for recording/reproduction of data has an oxygenconcentration distribution in a metal magnetic substance;

(12) a magnetic storage apparatus according to item (11), wherein therecording magnetic pole material of the magnetic head has oxygen-richparticles mixed of which the size is in a range between 0.5 nm and 5 nminclusive;

(13) a magnetic storage apparatus according to item (11), wherein theoxygen-rich particles mixed in the recording magnetic pole material ofthe magnetic head contain at least one of the elements Zr, Y, Ti, Hf, Aland Si;

(14) a magnetic storage apparatus according to item (8), wherein themagnetomotive force of the recording head for recording data or forrecording/reproduction of data, or the product of the recording currentand the number of turns of coil of the head is selected to be 0.5ampere•turn (AT) or above;

(15) a magnetic storage apparatus according to item (8), wherein atleast part of the recording magnetic poles of the magnetic head forrecording data or for recording/reproduction of data has a resistivityof 40 μΩ-cm or above and a relative permeability of 500 or above;

(16) a magnetic storage apparatus according to item (8), wherein atleast part of the recording magnetic poles of the magnetic head forrecording data or for recording/reproduction of data has a relativepermeability of 500 or below and a resistivity of 40 μΩ-cm or below;

(17) a magnetic storage apparatus according to item (8), wherein therise time of recording current is 5 nanosecond (ns) or below.

(18) a magnetic storage apparatus according to item (17), wherein therecording coil of an induction type magnetic head for recordinginformation on a magnetic disk medium is formed by a thin film processand has three terminals, and the inductance between the terminals is onemicrohenry (μH) or below;

(19) a magnetic storage apparatus according to item (18), wherein therecording coil 25″ (FIG. 9) of the induction type magnetic head forrecording information on the magnetic disk medium has a double-layerstructure in which the first layer coil 92 and the second layer coil 94have an equal number of turns but are wound in opposite directions toeach other;

(20) a magnetic storage apparatus according to item (18), wherein therecording coil 25′ (FIG. 8) of the induction type magnetic head used torecord information on the magnetic disk medium has a single-layerstructure 80 in which an intermediate-point terminal is connected at amid point (c) between both coil ends (a), (b) which mid pointcorresponds to half the total number of turns of the coil, and a current(FIG. 10) flowing between the terminals (c) and (a) is opposite in phaseto a current flowing between the terminals (c) and (b); and

(21) a magnetic storage apparatus according to item (8), wherein arecording/reproduction separation type head is provided which uses amagneto-resistive element, spin-valve element or giant magneto-resistiveelement for reproduction of information.

If the high-frequency loss (tan δ) in the magnetic film is due to onlythe eddy current loss, it can be expressed by $\begin{matrix}\begin{matrix}{{\tan \quad \delta} = {\mu^{''}/\mu^{\prime}}} \\{= {{R/\omega}\quad L}} \\{= {\mu_{0}\mu \quad \pi \quad d^{2}{f/C}\quad \rho}}\end{matrix} & (1)\end{matrix}$

where μ′ and μ″ are the real part and imaginary part of the complexpermeability, C is a constant depending on the film shape, and μ₀ is thepermeability of vacuum. By substituting the relative permeability μ,thickness d and resistivity ρ peculiar to the magnetic film intoEquation (1), it is possible to estimate the eddy current loss, tan δ ata frequency f. Since it can be considered that the change of headefficiency (efficiency for conduction of magnetic flux) to frequency isproportional to the change of the real part of the complex permeability,the frequency dependency of the head efficiency can be estimated fromthe cosine of the δ which is calculated from Equation (1). That is, thehead efficiency η at each frequency can be expressed by the followingequation:

η=cos[arc tan(μ₀ μπd ² f/Cρ)]  (2)

Thus, the head efficiency η at a given frequency f can be extrapolatedfrom the value μd²/ρ in Equation (2) where μ is the relativepermeability, d is the thickness and ρ is the resistivity, peculiar tothe magnetic film.

If this head is combined with a magnetic disk of a metal magnetic filmwhich has small writing blur or overwrite value variation at the time ofhigh frequency recording and of which the coercive force is 2 kOe orabove, it is possible to provide a high-performance magnetic storageapparatus capable of operating at an areal recording density of 500Mb/in² or above, recording frequency of 45 MHz or above and media datarate of 15 MB/s or above.

FIG. 7 shows the relation between the cost of input/output unit and thetransfer speed per magnetic disk storage apparatus which constitutes theinput/output unit, in which case a data bus of two-byte width Fast andWide SCSI (Small Computer System Interface) is used for the input/output(I/O) interface. From FIG. 7, it will be seen that when the data bus oftwo-byte width Fast and Wide SCSI interface is used, data transfer canbe made at a maximum of 20 MB/s. In this case, if the transfer speed permagnetic disk storage apparatus is 15 MB/s or above, the cost ofinput/output unit can be reduced.

Moreover, if the capacity per disk unit is 550 MB, it is possible tohandle OS (Operation Software) such as Windows or Workplace. In order torealize this capacity by a single 3.5-inch magnetic disk, it isnecessary that the areal data-recording density be selected to be 500Mb/in² or above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing measured results of the frequency-dependentrecording magnetic field which changes with electric characteristics andmagnetic characteristics of magnetic pole materials of thin-filmmagnetic heads, and calculated results of the head efficiency;

FIG. 2 is a graph showing the relation between the amount of attenuationof recording magnetic field and head performance index ξ at a recordingfrequency of 45 MHz;

FIGS. 3A and 3B are a plan view of a magnetic disk storage apparatusaccording to this invention, and a cross-sectional view taken along aline of arrows IIIA—IIIA in FIG. 3A, respectively;

FIG. 4 is a schematic view of the recording/reproduction separation-typehead mounted on the magnetic disk storage apparatus according to thisinvention;

FIG. 5 is a graph showing the relation between the rise time ofrecording current and overwrite characteristic value;

FIG. 6 is a graph showing the relation between the inductance of coiland the rise time of recording current; and

FIG. 7 is a graph showing the relation of input/output unit cost withrespect to the transfer speed per magnetic disk apparatus.

FIG. 8 is a view of a single layer, three terminal recording coil.

FIG. 9 is a view of a dual-layered, three terminal recording coil havinga first coil and a second coil wound in opposite directions.

FIG. 10 illustrates opposite phase currents flowing between terminals ofa three terminal recording coil.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(First Embodiment)

Three different induction-type thin-film magnetic heads were preparedwhich use magnetic poles of different resistivity ρ, film thickness d,and relative permeability μ. The frequency-dependency of the recordingmagnetic field intensity of each sample was measured by use of theelectron beam tomography method. The results are shown in FIG. 1. Table1 lists the magnetic materials used for each head, magnetic polethickness d, resistivity ρ, and relative permeability p in alow-frequency range of 1 MHz or below.

The head A has its magnetic poles made of an Ni—Fe single-layer film of3 μm in thickness. The head B has its poles made of a multi-layer of2.2-μm thick Co—Ni—Fe films with a 0.1-μm thick intermediate layer Al₂O₃interposed therebetween. Thus, the total thickness of the poles of thishead is 4.5 μm. In the multi-layer film of Co—Ni—Fe/Al₂O₃/Co—Ni—Fe, whenthe thickness of the single Co—Ni—Fe film is 2.7 μm or above, the rateof attenuation of the magnetic field intensity reaches 10% or above at arecording frequency of 45 MHz, and hence the writing blur, or overwritevalue is changed with recording frequency. Therefore, in thisembodiment, the thickness of the single Co—Ni—Fe film is selected to be2.2 μm. The head C has its magnetic poles made of a 3-μm thick Co—Ta—Zramorphous single-layer film of which the resistivity is 90 μΩ-cm.

TABLE 1 The characteristic values of materials of heads Pole Resist-Relative Magnetic thick- ivity Permea- mater- ness ρ bility ials d(μm)(μΩ-cm) μ For Head NiFe 3.0 16 1000 comp. A Embodi- B CoNiFe 2.2 16 1000ments multi- layer C CoTaZr 3.0 90 1000

FIG. 1 shows the measured results of the frequency dependency ofnormalized recording magnetic field intensity, and the calculatedresults of head efficiency η from Equation (2). From FIG. 1, it will beseen that as to the head A of Ni—Fe single-layer film magnetic pole, therecording field intensity is decreased at 10 MHz or above and reaches60% or below, at 100 MHz, as low as the intensity in the low-frequencyregion. On the other hand, as to the head B, the eddy current loss isremarkably decreased since the films Co—Ni—Fe are multilayered with theAl₂O₃ insulating layer interposed therebetween, though the permeabilityand resistivity of the Co—Ni—Fe film are equivalent to those of NiFefilm of head A. The attenuation of field intensity at 100 MHz, of thishead B is about 20%, or its frequency characteristic is improved. As tothe head C, the frequency characteristic is excellent since theattenuation of field intensity at 100 MHz is substantially zero. Theconstant C in Equation (2) is a parameter depending on the shape ofmagnetic poles. If C=14, the calculated results can be made wellcoincident with the experimental results.

Here, the head performance index ξ for indicating the degree ofdeterioration of the frequency characteristic of head recording fieldcan be defined as follows.

ξ=μd ²/ρ  (3)

Thus, the performance index ξ of each head listed in Table 1 can becalculated from Equation (3) as follows.

Head A; ξ=562.5

Head B; ξ=302.5

Head C; ξ=100

FIG. 2 show the measured results of the relation between the attenuationof field intensity and head performance index ξ at a recording frequencyof 45 MHz, of a large number of samples of thin-film magnetic heads withselected various different values of the thickness, resistivity andrelative permeability of magnetic poles. From FIG. 2, it will beunderstood that the attenuation of field intensity at a recordingfrequency of 45 MHz can be kept at 10% or below under the condition ofξ≦500.

(Second Embodiment)

A description will be made of a magnetic storage apparatus usingthin-film magnetic heads produced according to this embodiment. Amagnetic disk apparatus of this embodiment is schematically shown inFIGS. 3A and 3B. In FIGS. 3A and 3B, there are shown a magnetic head 10,a magnetic disk 11 of about 3.5 inch in outer diameter, a spindle 12 forrotating the disk, a positioning mechanism 13 for the magnetic head, anda housing 14. The magnetic head 10 is a self-recording/ reproductiontype head formed of induction-type elements for recording andreproduction, and it has a track width of 5.0 μm. The magnetic poles ofthe head are made of Co—Ta—Zr amorphous alloy thin film which has asaturation flux density of 1.3 Tesla, a resistivity p of 90 μΩ-cm, arelative permeability μ of 1000, and a thickness d of 3 μm. The gaplength of the head is 0.4 μm. The poles of the head may be made of othermaterials than Co—Ta—Zr amorphous alloy thin film, for example, anamorphous alloy thin film Fe—B—Si—C which has a saturation flux densityof 1.6 T or a multi-layer film of Co—Ni—Fe/Al₂O₃/Co—Ni—Fe or an Ni—Fefilm containing particles ZrO₂, Y₂O₃, TiO₂, HfO₂, Al₂O₃ or SiO₂ of 2 nmto 3 nm in diameter. In either case, the same effect as in thisembodiment can be achieved. It is experimentally confirmed that whenparticles of an oxide are mixed in the magnetic film, it is desirable toselect a diameter of 0.5 nm to 5 nm. The reason is that in this range ofparticle size, only the resistivity of magnetic film can be increasedwithout remarkable reduction of saturation flux density or soft magneticcharacteristic. Although the resistivity of an Ni—Fe film containingparticles ZrO₂, Y₂O₃, TiO₂, HfO₂, Al₂O₃ or SiO₂ of 2 nm to 3 nm size isincreased up to about 40 μΩ-cm, the relative permeability is around1000, and it exhibits good soft magnetic characteristic. When the polesof the magnetic head are made of an NiFe thin film containing no suchoxide, the high-frequency characteristic can be improved by decreasingthe relative permeability up to 500 or below. In this case, however, itis necessary that the recording magnetomotive force of the head beselected to be 0.5 AT or above.

The recording layer of the magnetic disk 11 is made of CoCrTa (theamount of Cr to be added is 16 atom. %) which has a coercive force of2100 Oe in the recording bit direction and a coercive force orientationratio of 1.2. The remanence-thickness product, Br•δ in this magneticdisk is 300 G•μm. By use of this recording medium it is possible toimprove the linear recording density characteristic and greatly reducethe medium noise in the high linear recording density region. If thecoercive force of the medium is 2000 Oe[Oersted] or below, the bit errorrate is reduced so that the storage apparatus cannot operate.

At the time of recording and reproduction, the spindle is rotated at arate of 4491 rpm (rounds per minute), and at this time the head at theoutermost periphery of the data-stored region is floated 0.05 μm abovethe magnetic disk. The recording frequency is so selected that thelinear recording density on each track is equal over the range from theinnermost periphery to outermost periphery of the data storing region.The recording frequency at the outermost periphery is 67.5 MHz.

In the magnetic disk storage apparatus of this embodiment, the lineardata-recording density on each track is 144 kBPI (kilo Bits Per Inch),the track density is 5 kTPI (kilo Tracks Per Inch), and the arealrecording density is 720 megabits per square inch. In this embodiment,four magnetic disks are used, the formatted capacity of the apparatus is2.8 gigabytes, and the data transfer speed is 15 megabytes per sec.Although this embodiment makes data recording by use of {fraction(8/9)}-code, data may be recorded by use of 1-7 RLL as in the prior art,in which case the same performance as in this embodiment can beachieved. In this case, however, the recording frequency is 45 MHz.

Table 2 lists the specifications of the magnetic storage apparatusaccording this embodiment.

TABLE 2 Specifications of 3.5-inch apparatus Storage capacity atformatting 2.8 GB Number of disks 4 Number of data surfaces 8 Number ofheads 8 Track number/disk surface 4427 Maximum linear recording density144 kBPI Track density 5 kTPI Rotational speed 4491 RPM Recordingfrequency 67.5 MHz Transfer speed (to/from Media) 15 MB/sec

(Third Embodiment)

A description will be made of the results of combining 2.5-inch,1.8-inch and 1.3-inch magnetic disks with the magnetic heads of theinvention in order to construct a magnetic storage apparatus. Themagnetic heads and magnetic disks used in this embodiment are the sameas in the second embodiment, the linear data-recording density on eachtrack is 144 kBPI, and the track density is 5 kTPI. Also, the rotationrate of the spindle is so selected that the transfer speed for each diskof different diameter is 15 MB/sec. In this embodiment, as is similar tothe second embodiment, data may be recorded by use of the conventional1-7 RLL, in which case the same performance as in this embodiment can beobtained. In this case, the recording frequency is 45 MHz. Tables 3 to 5list the specifications of each apparatus.

TABLE 3 Specifications of 2.5-inch apparatus Storage capacity atformatting 1.8 GB Number of disks 4 Number of data surfaces 8 Number ofheads 8 Track number/disk surface 2951 Maximum linear recording density144 kBPI Track density 5 kTPI Rotational speed 6736 RPM Recordingfrequency 67.5 MHz Transfer speed (to/from Media) 15 MB/sec

TABLE 4 Specifications of 1.8-inch apparatus Storage capacity atformatting 1.4 GB Number of disks 4 Number of data surfaces 8 Number ofheads 8 Track number/disk surf ace 2213 Maximum linear recording density144 kBPI Track density 5 kTPI Rotational speed 8982 RPM Recordingfrequency 67.5 MHZ Transfer speed (to/from Media) 15 MB/sec

TABLE 5 Specifications of 1.3-inch apparatus Storage capacity 0.9 GBNumber of disks 4 Number of data surfaces 8 Number of heads 8 Tracknumber/disk surface 1475 Maximum linear recording density 144 kBPI Trackdensity 5 kTPI Rotational speed 13473 RPM Recording frequency 67.5 MHzTransfer speed (to/from Media) 15 MB/sec

(Fourth Embodiment)

Although the magnetic storage apparatus of the first to thirdembodiments include induction-type self-recording/reproduction heads,recording/reproduction separation-type heads having magneto-resistiveelements (MR elements) for reproduction may be used to construct themagnetic storage apparatus with the same performance. FIG. 4 shows thestructure of the recording/reproduction separation-type head used inthis embodiment. In FIG. 4, there are shown a recording magnetic pole 20and an upper shield layer 21 which also serves as the other recordingmagnetic pole. These magnetic poles are made of anCo—Ni—Fe/Al₂O₃/Co—Ni—Fe multi-layered film of which the single Co—Ni—Felayer has a thickness of 2.2 μm. The thickness of the Al₂O₃ intermediatelayer is 0.1 μm, and the track width of the recording magnetic pole 20is 3 μm. A lower shield layer 22l is 1-μm thick and made of Ni—Fe alloy.A magneto-resistive element 23 is 15 nm thick and made of Ni—Fe alloy.This element 23 is driven by soft film biasing. The magneto-resistiveelement 23 may be made of other materials than Ni—Fe alloy. For example,it may be a spin-valve type element formed of Ni—Fe layer, Cu layer, Colayer and an Ni—O based, Fe—Mn based or Cr—Mn based antiferromagneticfilm or an alloy-based giant magneto-resistive element of Co—Ag, Co—Au,NiFe—Ag, Co—Cu, Fe—Ag or the like or a Co/Cr-, Fe/Cr- or Co/Cu-basedmulti-layered giant magneto-resistive element.

In FIG. 4, the region between a pair of electrodes 24 corresponds to thereproduction track width and is selected to have a width of 2 μm. In therecording mode, current of 15 mA op is caused to flow in a 20-turn coil25, thereby recording arbitrary information on a recording medium, ormagnetic layer. In the reproduction mode, a DC current of 8 mA is causedto flow in the lead wire 24, and detection is made of a leaking fieldfrom the magnetic medium layer.

This magnetic head is combined with a 3.5-inch magnetic disk in order toconstruct a magnetic storage apparatus. This disk has a recording layerof CoCrTa (the amount of Cr added is 16 atom. %). The coercive force ofthis layer in the recording bit direction is 2100 Oersted, and thecoercive force orientation ratio is 1.2. The remanence-thickness productBr•δ of the recording layer of the magnetic disk used here is 100 G•μm.Table 6 lists the specifications of the magnetic storage apparatusaccording to this embodiment.

TABLE 6 Specifications of 3.5-inch apparatus usingrecording/reproduction separation type head Storage capacity (atformatting) 5.5 GB Number of disks 4 Number of data surfaces 8 Number ofheads 8 Track number/disk surface 7378 Maximum recording density 170kBPI Track density 8.3 kTPI Rotational speed 4491 RPM Recordingfrequency 80.0 MHz Transfer speed (to/from Media) 18 MB/sec

(Fifth Embodiment)

A description will be made of the results of examining the effect of therise time of the recording current in the coil of the recording head onthe recording characteristics. FIG. 5 is a graph showing measuredoverwrite values with respect to rise time in a range from 2 ns to 10ns. In this case, after a high density, 144 kFCI, signal is overwrittenon a low density, 23 kFCI, signal, the amount of the erased part of thelow density signal is measured. The recording medium used for themeasurement is a CoCrTa-based spattered medium which has a coerciveforce of 2000 Oe[Oersted]. From the results, it will be seen that if therise time of the recording current is selected to be 5 ns or below, goodoverwrite characteristic can be obtained. In this experiment, three coilterminals were required in order for the rise time of the recordingcurrent to be 5 ns or below. FIG. 6 is a graph showing the relation ofthe rise time of recording current to the inductance of each coil. FromFIG. 6, it will be obvious that the inductance of each coil is requiredto be 1 μH (microhenry) or below in order for the rise time of recordingcurrent to be 5 ns or below.

According to this invention, since it is possible to use the magnetichead in which the recording field intensity is not attenuated even ifthe recording frequency exceeds 45 MHz, the magnetic storage apparatuscan rotate the disk at high speed, thereby achieving high speed transferof data, reduction of access time and increase of storage capacity at atime.

What is claimed is:
 1. A magnetic recording disk apparatus comprising: amagnetic head including a magnetic pole made of a material with aresistivity ρ(μΩ-cm) and with a relative permeability μ, achieving amedia data rate of 15 megabytes per second or greater and an areal datarecording density of 500 Mb/in² or greater, wherein said ρ, said μ and d(μm) which means the thickness of said magnetic pole satisfies therelation μd²/ρ<500.
 2. A magnetic recording disk apparatus according toclaim 1, wherein said magnetic film includes an oxide.
 3. A magneticrecording disk apparatus according to claim 2, further comprising, amagnetic disk of 3.5 inches or less in diameter, the magnetic diskrotating at a rate of 4000 rpm or greater, and a recording frequency ofthe magnetic disk being 45 MHz or greater.
 4. A magnetic recording diskapparatus according to claim 8, wherein said magnetic disk includes ametal magnetic layer of 2000 Oe or greater in coercive force.
 5. Amagnetic recording disk apparatus according to claim 2, wherein saidmagnetic head includes a reproduction head having at least one of amagneto-resistive effect element, a spin-valve element and a giantmagneto-resistive element.
 6. A magnetic recording disk apparatusaccording to claim 1, wherein said magnetic film is formed of at leastone of Zr, Y, Ti, Hf and Al, and an oxide of Si.
 7. A magnetic recordingdisk apparatus according to claim 6, further comprising, a magnetic diskof 3.5 inches or less in diameter, the magnetic disk rotating at a rateof 4000 rpm or greater, and a recording frequency of the magnetic diskbeing 45 MHz or greater.
 8. A magnetic recording disk apparatusaccording to claim 7, wherein said magnetic disk includes a metalmagnetic layer of 2000 Oe or greater in coercive force.
 9. A magneticrecording disk apparatus according to claim 6, wherein said magnetichead includes a reproduction head having at least one of amagneto-resistive effect element, a spin-valve element and a giantmagneto-resistive element.
 10. A magnetic recording disk apparatusaccording to claim 1, further comprising, a magnetic disk of 3.5 inchesor less in diameter, the magnetic disk rotating at a rate of 4000 rpm orgreater, and a recording frequency of the magnetic disk being 45 MHz orgreater.
 11. A magnetic recording disk apparatus according to claim 10,wherein said magnetic disk includes a metal magnetic layer of 2000 Oe orgreater in coercive force.
 12. A magnetic recording disk apparatusaccording to claim 1, wherein said magnetic head includes a reproductionhead having at least one of a magneto-resistive effect element, aspin-valve element and a giant magneto-resistive element.